Photochemical pump and NMR probe to monitor the formation and kinetics of hyperpolarized metal dihydrides

On reaction of IrI(CO)(PPh ) with para-hydrogen ( -H ), Ir(H) I(CO)(PPh ) is formed which exhibits strongly enhanced H NMR signals for its hydride resonances. Complex also shows similar enhancement of its NMR spectra when it is irradiated under -H . We report the use of this photochemical reactivity to measure the kinetics of H addition by laser-synchronized reactions in conjunction with NMR. The single laser pulse promotes the reductive elimination of H from Ir(H) I(CO)(PPh ) in C D solution to form the 16-electron precursor , back reaction with -H then reforms in a well-defined nuclear spin-state. The build up of this product can be followed by incrementing a precisely controlled delay ( ), in millisecond steps, between the laser and the NMR pulse. The resulting signal time profile shows a dependence on -H pressure. The plot of against -H pressure is linear and yields the second order rate constant, , for H addition to of (3.26 ± 0.42) × 10 M s . Validation was achieved by transient-UV-vis absorption spectroscopy which gives of (3.06 ± 0.40) × 10 M s . Furthermore, irradiation of a C D solution of with multiple laser shots, in conjunction with -H derived hyperpolarization, allows the detection and characterisation of two minor reaction products, and , which are produced in such low yields that they are not detected without hyperpolarization. Complex is a configurational isomer of , while is formed by substitution of CO by PPh .